refactor: Adapt to async version of spawn

[pgrzesik]

Related to: #646 - sync use of spawn prevented interactive output to be updated

[medikoo]

stdoutBuffer will be provided unconditionally, so no need to confirm on it

[pgrzesik]

Is that the same case with stderrBuffer?

[medikoo]

Yes, but in case of error handling, there could be an edge case, where the command fails because it cannot be invoked for some reason and then the error won't hold any of those properties

[medikoo]

More natural would be includes('--system')

[medikoo]

Looks great 👍

[obataku]

@pgrzesik which version of nodejs supports Buffer.trim? not seeing it in 17.x

[pgrzesik]

Hello @obataku - I believe it's not supported at all on Buffer, are you observing some issues or such usage?

[obataku]

@pgrzesik indeed, using dockerizePip with serverless-python-requirements@5.2.1 gives the following error:

  TypeError: ps.stdoutBuffer.trim is not a function
      at getDockerUid (.../node_modules/serverless-python-requirements/lib/docker.js:200:26)
      at async installRequirements (.../node_modules/serverless-python-requirements/lib/pip.js:341:30)
      at async installRequirementsIfNeeded (.../node_modules/serverless-python-requirements/lib/pip.js:682:3)
      at async ServerlessPythonRequirements.installAllRequirements (.../node_modules/serverless-python-requirements/lib/pip.js:760:29)

... which points to the following change introduced by this PR: https://github.com/serverless/serverless-python-requirements/blame/e3d9ebcdd3ec72cc2e3301d33e10dd10ef6a594d/lib/docker.js#L200

-  return ps.stdout.trim();
+  return ps.stdoutBuffer.trim();

[pgrzesik]

Thanks for reporting, I see the issue now where the stdout was string (surprisingly it could also be a Buffer but for some reason it worked). I will prepare a fix for it and issue a new release 👍